Colorado Hopes This Asian Wasp Can Save its Trees

Researchers are hoping to use one non-native species to fight another, more destructive one

emerald ash borer
An emerald ash borer, the problem the wasp is supposed to address US Department of Agriculture/Flickr (CC BY 2.0)

The trees in Colorado* are under threat. They are in danger of succumbing to the same invader that is felling ash trees around the country: the invasive emerald ash borer. Things are desperate enough that Colorado is now using fire to fight fire — a predator wasp from China has just been unleashed in Boulder in the hopes that this foreign species will destroy the other, reports Bruce Finley for The Denver Post. 

The ash borers, with their jewel-like green carapaces, also hail from Asia. The first reports in the U.S. started rolling in from the Midwest in 2002, but the insect probably arrived in North America through packing crates sometime in the late 1990s. The larvae live beneath bark and snack on the tree’s tender, living tissues, slowly killing the tree from the inside out. In its native range, resistant trees and predators keep the beetle in check. In North America the beetles run rampant, killing nearly all trees after just six years in an area.

The wasp, Oobius agrili, is one of the predators that keeps the beetle at bay in Asia. It lays its eggs on the beetle's eggs. Once they hatch, wasp larvae eat the baby beetles before they can emerge. But researchers don’t know yet if the wasp release in Boulder will work. "This is an experiment. We hope it is enough and that the wasps will establish themselves. The idea is they will reproduce on their own,"  John Kaltenbach with state Department of Agriculture told Finely. The experts hope that the wasp will survive the winter and then work to save the estimated 1.45 million ash trees in the Denver metro area.

In Minneapolis, a different predatory wasp appears to be working to curb the beetle's destruction. And sometimes pitting one invasive against another (even inadvertently) does work: Crazy ants might be beating back invasive fire ants. But it’s hard to be absolutely sure that any non-native species introduction won’t have unintended consequences. Some people even argue that there is value in not eliminating invasive species.

Still, since humans tend to value one species over another, the demand for creative solutions is high. Even if that includes eating the invasives.

*An earlier version of this story misidentified the city in which the wasps were released. They were unleashed by the Colorado Department of Agriculture in Boulder, not Denver. We regret the error. 

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